JP2007249093A - Wavelength filter, wavelength filtering method, and wavelength filtering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength filter achieving wavelength filtering of a narrow band at a low cost and to provide wavelength filtering method and apparatus using the wavelength filter. <P>SOLUTION: The wavelength filter reducing intensity of reflection light having a specific wavelength and provided with a light transmissible member equipped with an incident part, an emission part and a reflection surface to incident light from the incident part, a metal thin film provided on the outer side of the reflection surface and a dielectric thin film provided on the outer side of the metal thin film is characterized in that the metal thin film has 10 to 100 nm thickness and the dielectric thin film has 200 to 20,000 nm thickness. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavelength filter for reducing the light intensity in a specific wavelength region.

  In recent years, wavelength division multiplexing has become mainstream in optical information communication. In this method, a method of switching or blocking a transmission path for only an optical signal having a specific wavelength is employed. Various wavelength filters have been proposed for this purpose. Typical examples are those using a diffraction grating (Patent Document 1), those using a superlattice structure (Patent Document 2), and ring waveguides. There are those to be used (Patent Document 3) and those having a dielectric multilayer film (Patent Document 4).

However, since the thing of patent document 1 uses a diffraction grating, a filtering wavelength will be fixed and must produce a diffraction grating for every required filtering wavelength. Patent Documents 2 and 3 use a superlattice structure and a ring-shaped waveguide, resulting in high manufacturing costs. In addition, in Patent Document 4, a layer having an electro-optic effect is interposed, and the filtering wavelength is changed by electric field load so as to broaden the filtering characteristics. In the end, the manufacturing cost is increased.
On the other hand, surface plasmon resonance (SPR) is known as a resonance phenomenon in which surface plasmon polariton (or simply surface plasmon), which is an electron wave on a metal surface, interacts with light, resulting in unique absorption. (For example, non-patent documents 1 to 4). However, the range of absorption wavelength due to surface plasmon resonance is as wide as about 50 nm, and its use is limited, such as low applicability to wavelength multiplexing communications.
JP 2004-12658 A JP 2003-66386 A JP 2004-279882 A JP 2001-21852 A M. Osterfeld et al., Applied Physics Letter, 62 (1993) 2310-2312 X.-M.Zhu et al., Sensors and Actuators B, Volume 84 (2002) pp. 106-112 K. Kurosawa et al., Physical Review B, Volume 33 (1986) 789-798 S. Ekgasit et al. Applied Spectroscopy, 59 (2005) 661-667

  It is an object of the present invention to provide a wavelength filter capable of eliminating these problems of the prior art and performing wavelength filtering in a narrow band at low cost, and a wavelength filtering method and apparatus using the wavelength filter. .

  In order to achieve the above object, the present invention is a wavelength filter that reduces the intensity of reflected light of a specific wavelength, and includes an incident part, an emitting part, and a light-transmissive member that has a reflecting surface for incident light from the incident part. And a metal thin film provided outside the reflective surface and a dielectric thin film provided outside the metal thin film, wherein the metal thin film has a thickness of 10 to 100 nm, and the thickness of the dielectric thin film The present invention provides a wavelength filter having a thickness of 200 to 20000 nm.

  In order to achieve the above object, the present invention also provides a leaky mode using the wavelength filter, allowing light to be incident from the incident portion so as to cause total reflection at the reflecting surface, and incidental to surface plasmon resonance on the reflecting surface. The present invention provides a wavelength filtering method characterized in that reflected light is emitted from the emitting portion.

  In order to achieve the above object, the present invention also provides a wavelength filtering device comprising: the wavelength filter; and an angle adjusting device provided to change an angle formed between incident light and the reflecting surface. It is to provide.

  The wavelength filter according to the present invention includes an incident part, an emitting part, a light transmissive member having a reflection surface for incident light from the incident part, a metal thin film provided outside the reflection surface, and the metal thin film. And a dielectric thin film provided on the outside. Therefore, when light is incident on the wavelength filter from the incident portion so as to cause total reflection on the reflection surface, surface plasmon resonance can be generated on the reflection surface.

  In particular, in the present invention, the generation of surface plasmon resonance is ensured by setting the thickness of the metal thin film to 10 to 100 nm, and then the surface plasmon resonance is set by setting the thickness of the dielectric thin film to 200 to 20000 nm. A leaky mode accompanying the resonance appears, and the relationship between the incident angle and wavelength (dispersion characteristic) of the leaky mode is used. Non-Patent Document 1 introduces a leaky mode using a monochromatic laser. Since the absorption wavelength band in the leaky mode is narrow, the intensity of only the specific narrow band of the reflected light from the reflecting surface is reduced. Therefore, this wavelength filter is optimal for applications that require wavelength filtering in a narrow band, such as wavelength multiplex communication. In addition, the appropriate film thickness and effect of these metal thin films and dielectric thin films will be described in detail in the description of the following embodiments.

  Further, this wavelength filter has an advantage that the manufacturing cost is low because a metal thin film and a dielectric thin film may be formed on the light transmissive member. Furthermore, as will be described later, since various wavelength absorption characteristics can be obtained by changing the film thickness of the dielectric thin film in the wavelength filter, it is possible to easily design the wavelength filter according to the application. In addition, since the absorption wavelength range can be changed greatly only by changing the incident angle with respect to the reflecting surface, filtering according to the situation can be easily performed with one wavelength filter.

  In the wavelength filtering method, filtering utilizing the characteristics of the wavelength filter can be performed by using the reflected light in the leaky mode in the wavelength filter of the present invention as outgoing light.

  The wavelength filtering device has a simple structure in which an angle adjusting device that changes the angle formed by incident light and the reflecting surface is combined with one or a plurality of wavelength filters of the present invention. Changes can be made quickly depending on the situation.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same or similar parts in the drawings may be denoted by the same reference numerals and description thereof may be omitted.

FIG. 1 is a diagram schematically showing an embodiment of a wavelength filter according to the present invention. In this embodiment, a quartz glass prism 4 is used as a light transmissive member (substrate), one side surface of the prism 4 is an incident portion 41, the other side surface is an output portion 42, and the bottom surface is a reflection surface 43 for incident light. Yes. The metal thin film 3 is provided outside the reflecting surface 43, and the dielectric thin film 2 is provided outside the metal thin film. Furthermore, in this example, the polarizing element 5 is provided in the incident portion 41, and P-polarized light passes through the polarizing element 5 in the white light from the incident light source 1. A parallel light beam is emitted from the light source 1 so as to be totally reflected by the reflecting surface 43. These portions correspond to the layer structure for calculating the dispersion characteristics of surface plasmon resonance and incidental leaky mode, and include air (medium 1), dielectric thin film (medium 2), metal thin film (medium 3), light The transparent member (medium 4) constitutes each layer. The calculation of the dispersion characteristic will be described later.

  As a material constituting the prism 4 (light transmissive member), light transmissive materials such as various glasses and plastics can be used in addition to quartz glass. The form of the light transmissive member is not limited to the prism, and it is sufficient that incident light can be guided to the reflecting surface, and various forms such as a plate shape and a block shape can be used. Further, a flat light-transmitting plate can be joined to the surface of a light-transmitting member main body such as a prism, and the outer surface of the plate can be used as a reflecting surface. The plate is preferably made of the same material as the light transmissive member main body, but may be made of other materials.

  Light incident on the prism 4 from the light source 1 through the polarizing element 5 is totally reflected by the reflecting surface 43. At this time, since the metal thin film 3 and the dielectric thin film 2 are provided outside the reflection surface, surface plasmon resonance occurs due to the interaction between the electron wave on the metal surface and light. In order to reliably obtain surface plasmon resonance at the reflecting surface 43, the metal thin film 3 has a thickness of 10 to 100 nm. If the thickness of the metal thin film 3 is less than 10 nm, the effect of metal electrons is low and sufficient surface plasmon resonance cannot be obtained. If the thickness exceeds 100 nm, the amount of attenuation of the evanescent wave propagating in the metal layer increases, and sufficient surface plasmon resonance cannot be obtained.

  As a material for forming the dielectric thin film 2, various light transmissive materials such as glass and plastic can be used. Further, it is desirable that the dielectric thin film has a refractive index equivalent to or close to that of the light transmissive member. This is because the relationship between wavelength and angle in the dispersion characteristics of surface plasmon resonance tends to be linear. From this point of view, it is desirable that the dielectric thin film is made of the same material as the light transmissive member.

  The thickness of the dielectric thin film 2 is 200 to 20000 nm. By providing such a thick dielectric layer, a leaky mode associated with surface plasmon resonance can appear. FIG. 2 is a graph showing the state of surface plasmon resonance when the dielectric thin film is not provided on the prism (a) and when it is provided (b). In the graph, the horizontal axis represents the incident angle with respect to the reflecting surface 43, and the vertical axis represents the wavelength of incident light. The curved black portion represents a band where the reflected light intensity is low, that is, an absorption wavelength band. When the dielectric thin film is not provided (a), only an absorption band (SPR) due to surface plasmon resonance occurs. On the other hand, when a dielectric thin film is provided, the absorption band SPR due to surface plasmon resonance moves to the right on the graph, and an absorption band due to leaky mode appears. Then, as the thickness of the dielectric thin film is increased, these curves move to the right, and primary, secondary,..., N-th leaky modes appear from the left on the graph one after another. In the state of FIG. 2B, the absorption band SPR due to surface plasmon resonance moves to the right and disappears outside the display range of the graph, and the primary leaky mode (LM1) and the secondary leaky mode (LM2) appear. Show. In this example (b), a silver thin film (thickness 50 nm) is provided on the reflection surface of the quartz prism, and a quartz dielectric thin film (thickness 500 nm) is provided thereon.

FIG. 3 shows the absorption characteristics when the silver thin film (50 nm) and the quartz thin film are provided on the quartz prism and the incident angle is 60 ° and the thickness of the quartz thin film is changed. The horizontal axis indicates the thickness of the quartz thin film, the left vertical axis corresponds to the solid line graph curve with the filter peak wavelength (wavelength indicating the maximum absorbance), and the right vertical axis indicates the spectral width (absorption wavelength band). Corresponds to the dashed graph curve. As can be seen from this graph, when the thickness of the quartz thin film is 50 nm, absorption is caused by surface plasmon resonance (SPR), and the absorption band has a wide spectral width (half-value width) of about 50 nm. On the other hand, in the leaky mode (LM1, LM2, LM3) when the thickness of the quartz thin film exceeds 300 nm, the spectrum width is as narrow as about 10 nm or less, and absorption in a narrow band is possible. This point can also be shown by FIG. 7 and FIG. 7 and 8 show the relationship between the wavelength (horizontal axis) and the reflectance (vertical axis) when the incident angle is 60 ° for the same object used in the case of FIG. 7 shows the absorption wavelength band (rough dotted line graph on the right side) in the leaky mode (LM1) when the thickness of the quartz thin film is 500 nm, and FIG. 8 shows the surface plasmon resonance (SPR) when the thickness of the quartz thin film is 50 nm. The absorption wavelength band is shown. As shown in these figures, when the thickness of the quartz thin film is as thin as 50 nm, the spectral width of the absorption band is as wide as about 40 nm, and when the thickness of the quartz thin film is 500 nm, the spectral width is 10 nm. It is narrower to a degree or less.

  FIG. 4 is a graph showing the characteristics shown in FIG. 3 in relation to the thickness of the dielectric thin film (vertical axis) and the peak angle (incident angle / horizontal axis indicating the maximum value of absorbance). Efficient absorption can be obtained by setting the film thickness of the dielectric thin film according to this graph and selecting the incident angle. 5A shows that the absorption bands of the primary and secondary leaky modes LM1 and LM2 extend beyond 800 nm, and FIG. 5B shows that the absorption band of the primary leaky mode is close. It shows that the infrared light communication band extends to 1700 nm. In the example of FIG. 5, a silver thin film (thickness 50 nm) is provided on the reflection surface of the quartz prism, and a quartz dielectric thin film (thickness 1000 nm) is provided thereon.

  The thickness of the dielectric thin film 2 is set to 200 to 20000 nm in consideration of the appearance of the leaky mode as described above, and the leaky mode cannot be appropriately obtained when the thickness of the dielectric thin film is less than 200 nm. This is because if the film thickness exceeds 20000 nm, sufficient absorption characteristics in the leaky mode cannot be obtained. From this viewpoint, the thickness of the dielectric thin film is more preferably 300 to 2000 nm, and further preferably 400 to 1200 nm.

  As the metal forming the metal thin film, silver shows the best absorption characteristics, and gold, aluminum, and copper also show the absorption characteristics next to them. Silver, aluminum, and copper are chemically less stable than gold. However, in the present invention, the metal thin film is covered with a dielectric thin film, so that these metals are also stable against oxidation.

  As described above, the metal thin film has a thickness of 10 to 100 nm in order to obtain sufficient surface plasmon resonance. However, the filtering characteristic can be selected according to the setting of the thickness. Hereinafter, a description will be given with reference to FIG. FIG. 6 shows the relationship between the thickness of the silver thin film (horizontal axis), the minimum reflectance (left vertical axis), and the angle of incidence at the minimum reflectance (right vertical axis). The vertical axis and the dashed graph curve correspond to the right vertical axis. Here, the dielectric thin film is formed of quartz glass to a thickness of 500 nm. As shown in this figure, for example, by setting the incident angle to 60 ° and setting the thickness of the silver thin film to 10 nm or 90 nm, the minimum reflectance can be about 85%. Further, by setting the thickness to 25 or 70 nm, 35 or 60 nm, or 40 to 55 nm, the minimum reflectance can be reduced to about 50%, about 20%, or about 10% or less, respectively. In the case of other incident angles and other metals, a graph similar to that in FIG. 6 can be obtained, and based on this, the film thickness for obtaining a desired minimum reflectance can be set. In addition, the reflectance described in this specification and a claim means the reflectance in the reflective surface of a light transmissive member unless there is particular notice.

Furthermore, the absorption wavelength band can be changed by changing the incident angle with respect to the reflection surface of the wavelength filter. FIG. 7 shows the relationship between wavelength (horizontal axis) and reflectance (vertical axis) for three incident angles (indicated by three types of lines). As seen in this graph, the absorption wavelength band can be changed to about 630 nm, about 545 nm, and about 460 nm by changing the incident angle to 60 °, 65 °, and 70 °. Therefore, if the incident angle is changed by means such as rotating the wavelength filter, it is possible to easily switch to a plurality of types of absorption wavelength bands with a single wavelength filter. The wavelength filter used here has a silver thin film of 45 nm and a quartz thin film of 500 nm formed on the reflection surface of the quartz prism.

  The wavelength filter can also change the absorption wavelength band by changing the thickness of the dielectric thin film. FIG. 9 shows the relationship between wavelength (horizontal axis) and reflectance (vertical axis) for three types of dielectric thin film thicknesses (indicated by three types of lines). As seen in this graph, the absorption wavelength band can be changed by changing the thickness of the dielectric thin film to 500 nm, 2000 nm, and 3000 nm. Here, a silver thin film is formed to a thickness of 50 nm on a quartz prism, and the incident angle with respect to the reflecting surface is set to 60 °.

  Furthermore, the selectivity of the wavelength to be attenuated can be expanded by combining a plurality of wavelength filters. FIG. 10 shows the wavelength of reflected light (horizontal axis) when two wavelength filters are arranged in series for one incident light, and the incident angles on the respective reflecting surfaces are set to 60 ° and 58 °. The relationship with the reflectance (vertical axis) is shown. With this combination, a plurality of absorption wavelength bands arranged in a comb shape can be obtained from each of the two wavelength filters and alternately arranged. As a result, the arrangement of the absorption wavelength band can be refined, and the selectivity of the absorption wavelength band is expanded.

  The dielectric thin film in the wavelength filter is preferably made of the same material as that of the light-transmitting member or a material having a refractive index close to the point that the relationship between the wavelength and angle in the dispersion characteristic of surface plasmon resonance tends to be linear. However, a good absorption band can be obtained to some extent even when different materials are used. In FIG. 11, quartz and acrylic are used as the light transmissive member, a silver thin film is formed with a thickness of 50 nm on each, and a dielectric thin film provided thereon is made of quartz and acrylic, and dispersion characteristics are shown for all combinations of materials. It is shown. In the graph, the horizontal axis represents the incident angle and the vertical axis represents the wavelength, and the drawn curve represents the absorption wavelength band. As shown in these graphs, the primary leaky mode (LM1) and the secondary leaky mode (LM2) are well generated in any combination of the light transmissive member and the dielectric thin film.

When forming the metal thin film of the wavelength filter, another metal can be interposed between the metal that should generate surface plasmon resonance and the light transmissive member. The bondability of the metal thin film to the member can be improved. For example, in Non-Patent Document 4, a chromium film is interposed to improve the bondability between glass and a gold thin film.
The thickness of the intervening metal layer is set to such an extent that an effect of improving the bonding property is obtained and excitation of surface plasmons by the target metal thin film is not hindered.

  FIG. 12 shows a wavelength filter in which a 50 nm silver thin film is formed on a quartz prism through a gold intervening layer, and a quartz thin film is formed thereon with a thickness of 500 nm. The dispersion characteristics when the thickness is 10 nm, 20 nm, and 30 nm are shown. As shown in this figure, the reflectance can be suppressed to about 60% even when the thickness of the intervening layer is 30 nm.

  FIG. 13 shows dispersion characteristics when the intervening metal is aluminum and the thickness of the intervening layer is 10 nm, 20 nm, and 30 nm in the same configuration as in FIG. As shown in this figure, the reflectance can be suppressed to about 50% even when the thickness of the intervening layer is 10 nm.

  By using the wavelength filter according to the present invention described above, light is incident from the incident part so as to cause total reflection on the reflecting surface, and the leaky mode reflected light incident on the surface plasmon resonance on the reflecting surface is emitted from the emitting part. Therefore, it is possible to obtain an effect that wavelength filtering in a narrow band can be performed at low cost.

  Further, by using the wavelength filter of the present invention and by providing an angle adjusting device so as to change the angle formed between the incident light and the reflecting surface, a wavelength filtering device can be configured, with a simple structure and an absorption wavelength range. It becomes possible to make a quick change according to the situation.

FIG. 14 shows wavelength filtering using a wavelength filter in which a metal thin film 3 and a dielectric thin film 2 are formed on one surface of a light transmissive member 4 ′ having a parallelogram cross section and a polarizing element 5 is provided on an adjacent surface. 1 schematically shows an example of an apparatus. This wavelength filtering device includes a rotating shaft 6 extending perpendicularly to a plane (incident surface) including incident light and reflected light, and the rotating shaft is coupled to a wavelength filter and wavelength around the rotating axis by a driving device (not shown). The filter is configured to rotate to a desired angle. The rotating shaft 6 may be directly coupled to the light transmissive member 4 ′ of the wavelength filter, or may be attached to a member that supports the wavelength filter. The incident light (Σλ) to the wavelength filter is in a state where the absorption wavelength band (λ1) is filtered by the reflecting surface 43 ′, and output light (Σλ-λ1) is obtained. Then, if the wavelength filter is rotated by a certain angle around the rotation axis 6, the incident angle of the incident light with respect to the reflecting surface 43 ′ can be changed, and the absorption wavelength band (λ1) is changed accordingly. As a result, output light (Σλ−λ1) including different cut wavelengths is obtained.

  Furthermore, various wavelength filtering can be performed using the characteristics of the wavelength filter according to the present invention. FIG. 15 shows a wavelength filtering apparatus as an example. In the apparatus of FIG. 15A, the cross-sectional shape of the light transmissive member 4a (substrate) is a wedge shape, and is tapered from the incident side to the emission side. A metal thin film 3a and a dielectric thin film 2a having a constant thickness are provided on one side surface, and a polarizing element 5 is disposed on the incident side end surface as necessary. The light incident from the end face of the light transmissive member 4a changes its traveling angle every time it undergoes total reflection between the facing side faces. That is, the incident angle to the metal thin film 3a changes one after another, and the absorption wavelength band changes one after another accordingly. As a result, light in which the absorption wavelength band (λ1 to λn) that has acted in the optical path is cut or reduced is obtained as output light. Note that each of “λ1” to “λn” described in FIG. 15 collectively represents a plurality of absorption wavelength bands obtained at one reflection location in the wavelength filter, and subscripts 1 to n are The order of reflection locations for incident light is shown.

  In the apparatus of FIG. 15B, the light transmissive member 4b has side surfaces facing in parallel, and a metal thin film 3b having a constant thickness and a plurality of dielectric thin films 2b1 to 2bn are provided on one side surface. . These dielectric thin films are arranged from the incident side to the emission side, and the respective thicknesses are sequentially reduced. Accordingly, the light incident from the end face of the light transmissive member 4b is subjected to the action of the dielectric thin films 2b1 to 2bn having different thicknesses every time the total reflection is repeated between the facing side faces. That is, the function of a wavelength filter having a different absorption wavelength band for each section is received. As a result, light in which the absorption wavelength band (λ1 to λn) that has acted in the optical path is cut or reduced is obtained as output light.

  In the apparatus of FIG. 15 (c), the light transmissive member 4c has side surfaces facing in parallel, and one side surface has a metal thin film 3c having a constant thickness and a thickness continuously from the incident side to the emission side. A thinned dielectric thin film 2c is provided. Accordingly, the light incident from the end face of the light transmissive member 4c is subjected to the action of different thickness portions in the dielectric thin film 2c every time the total reflection is repeated between the facing side faces. That is, a filter function showing an absorption wavelength band (λ1 to λn) that differs depending on the portion is received. As a result, light in which the absorption wavelength band (λ1 to λn) that has acted in the optical path is cut or reduced is obtained as output light.

According to the embodiment shown in FIG. 15, a variety of filtering functions can be obtained with a single wavelength filter, which is suitable as a wavelength filter for wavelength multiplexing communication that requires a low cost and a compact shape. is there. In these embodiments, the direction of taper of the light transmissive member and the direction of change in thickness of the dielectric thin film can be reversed. Further, different specifications in FIGS. 15A, 15B, and 15C can be combined as appropriate.
The present invention is not limited to the above embodiment, and various modifications can be made. In the embodiment shown in FIGS. 14 and 15, the metal thin film and the dielectric thin film are provided on one surface of the light transmitting member. However, the metal thin film and the dielectric thin film are also provided on the surface facing the surface. It is also possible to provide a filter action every time incident light is totally reflected. In this case, the metal thin film and the dielectric thin film provided on the opposing surfaces can have different thicknesses, tapers, etc., and the materials of the films can be made equal or different.

  Moreover, the incident light to the wavelength filter can be not only P-polarized light but also S-polarized light. However, excellent filter characteristics can be obtained when P-polarized light is used.

  Furthermore, the polarizing element may be installed in any one of the incident light path and the reflected light path, such as being provided in the light emitting part in addition to the light incident part of the wavelength filter. Alternatively, if polarized light such as a laser is used as incident light, the polarizing element can be omitted.

A method for calculating the dispersion characteristics (relationship between wavelength and incident angle) of surface plasmon resonance and the accompanying leaky mode will be described below. This dispersion characteristic is the solution of Maxwell's equation. As a method of solving Maxwell's equation, the matrix method can derive the relationship of the reflectance of electromagnetic waves in a multilayer thin film. The method for obtaining the reflectance is described in detail in Non-Patent Document 3. In the n-layer structure of the multilayer film as shown in FIG. 16, an electromagnetic wave propagating through the multilayer film having the n-layer structure is assumed. The laminated films are stacked in the z-axis direction, and the x and y-axis directions are semi-infinite. Z-direction of the first layer and the n layer becomes z → -∞ and z → ∞, z _1, z ₂ as an intermediate layer, ..., are linked in the z _n-1. The dielectric constant is ε (1), ε (2), ...
As ε (n), the thickness of the j-th layer is given by (Equation 1).

この構造では、表面プラズモンは光の波数ベクトルｋ_//とともにx軸方向に伝搬する。
振動数ωでｊ番目の層における伝搬の式は（式２）で与えられる。

In this structure, the surface plasmon propagates in the x-axis direction together with the light wave vector k _// .
The equation of propagation in the jth layer at the frequency ω is given by (Equation 2).

ここで、積層方向（ｚ軸）方向に沿った波数ｋ_z(j)は（式３）で与えられ、積層面内方向に沿った波数ｋ_//(ｊ)は（式４）で与えられる。

Here, the wave number k _z (j) along the stacking direction (z-axis) is given by (Expression 3), and the wave number k _// (j) along the in-stack direction is given by (Expression 4). .

ただし、ｎ_n（またはε_n）はプリズムの波長λに対する屈折率（誘電率）、ｋ₀は入射
光（振動数ω₀）の真空中での波数（2π/λ₀）、cは真空中の光速度、A_μ(j)は反射、B_μ(j)は入射あるいは透過の電場の振幅ベクトルである。

Where n _n (or ε _n ) is the refractive index (dielectric constant) with respect to the wavelength λ of the prism, k ₀ is the wave number (2π / λ ₀ ) of the incident light (frequency ω ₀ ) in vacuum, and c is in vacuum Of light, A _μ (j) is the reflection, and B _μ (j) is the amplitude vector of the incident or transmitted electric field.

In the case of P-polarized light (Transverse Magnetic: TM) with an electric field direction in the drawing, M _TM is a matrix shown in (Equation 5), and reflectivity considering the laminated structure by (Equation 2) and (Equation 6). R is given by (Equation 7).

また、Ｐ偏光（TM）と同様、図面内にある入射面内に垂直な方向に電場方向があるS偏
光(Transverse Electric: TE)の反射率Ｒは、（式8）に示すM_TEを使って計算できる。

Similarly to P-polarized light (TM), the reflectivity R of S-polarized light (Transverse Electric: TE) with an electric field direction perpendicular to the plane of incidence in the drawing uses the M _TE shown in (Equation 8). Can be calculated.

It is a figure which shows roughly one Embodiment of the wavelength filter which concerns on this invention. It is a graph which shows the state of surface plasmon resonance divided into the presence or absence of a dielectric thin film. It is a graph which shows the absorption characteristic at the time of changing the thickness of a quartz thin film regarding the wavelength filter of this invention. It is a graph which shows the relationship between the film thickness of a dielectric thin film, and an absorption peak angle regarding the wavelength filter of this invention. Regarding the wavelength filter of the present invention, (a) is a graph showing the absorption bands in the first and second leaky modes, and (b) is a graph showing the absorption bands in the first leaky mode. It is a graph which shows the relationship between the incident angle in the thickness of a silver thin film, minimum reflectance, and minimum reflectance regarding the wavelength filter of this invention. It is a graph which shows the relationship between a wavelength and a reflectance about a wavelength filter of this invention about a different incident angle. It is a graph which shows the absorption wavelength band by surface plasmon resonance (SPR). It is a graph which shows the relationship between a wavelength and a reflectance about the wavelength filter of this invention about different dielectric material thin film thickness. It is a graph which shows the relationship between a wavelength and a reflectance when two wavelength filters are arrange | positioned in series at a different angle regarding the wavelength filter of this invention. It is a graph which shows the dispersion characteristic when the light-transmitting member and a dielectric thin film are made into the same or different material regarding the wavelength filter of this invention. It is a graph which shows the dispersion characteristic at the time of providing the intervening layer of gold | metal | money between a prism and a metal thin film regarding the wavelength filter of this invention. It is a graph which shows the dispersion characteristic at the time of providing the intervening layer of aluminum between the prism and the metal thin film regarding the wavelength filter of this invention. It is a figure which shows roughly an example of the wavelength filtering apparatus which concerns on this invention. It is a figure which shows roughly the other example of the wavelength filtering apparatus which concerns on this invention. It is explanatory drawing for calculation of the dispersion characteristic of surface plasmon resonance and leaky mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Dielectric thin film 3 Metal thin film 4 Prism (light transmissive member)
5 Polarizing element 41 Incident part 42 Emission part 43, 43 'Reflecting surface LM1, LM2, LM3 Leaky mode

Claims (4)

A wavelength filter for reducing the intensity of reflected light of a specific wavelength, provided on the outside of the reflecting surface, the light transmitting member having an incident portion, an emitting portion, and a reflecting surface for incident light from the incident portion. A metal thin film and a dielectric thin film provided outside the metal thin film, wherein the metal thin film has a thickness of 10 to 100 nm, and the dielectric thin film has a thickness of 200 to 20000 nm. Wavelength filter to be used. The wavelength filter according to claim 1, wherein the metal thin film is silver, gold, aluminum, or copper. The wavelength filter according to claim 1, wherein light is incident from the incident portion so as to cause total reflection on the reflection surface, and the leaky mode reflected light incident to surface plasmon resonance on the reflection surface is emitted. The wavelength filtering method characterized by making it radiate | emit from a part. 3. A wavelength filtering device comprising: the wavelength filter according to claim 1; and an angle adjusting device provided so as to change an angle formed between incident light and the reflecting surface.

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